Recombinant poxviruses are widely used to express foreign antigens in infected cells. Moreover, recombinant poxviruses are currently tested as very promising vaccines to induce an immune response against the foreign antigen expressed from the poxvirus vector. Most popular are avipoxviruses on the one side and vaccinia viruses, in particular Modified vaccinia virus Ankara (MVA) on the other side. MVA is related to vaccinia virus, a member of the genera Orthopoxvirus in the family of Poxviridae. MVA has been generated by 516 serial passages on chicken embryo fibroblasts of the Ankara strain of vaccinia virus (CVA) (for review see Mayr, A., et al. Infection 3, 6-14 [1975]). As a consequence of these long-term passages the resulting MVA virus deleted about 31 kilobases of its genomic sequence and, therefore, was described as highly host cell restricted to avian cells (Meyer, H. et al., J. Gen. Virol. 72, 1031-1038 [1991]). It was shown, in a variety of animal models that the resulting MVA was significantly aviruient (Mayr, A. & Danner, K. [1978] Dev. Biol. Stand. 41: 225-34). Additionally, this MVA strain has been tested in clinical trials as vaccine to immunize against the human smallpox disease (Mayr et al., Zbl. Bakt. Hyg. I, Abt. Org. B 167, 375-390 [1987], Stickl et al., Dtsch. med. Wschr. 99, 2386-2392 [1974]).
U.S. Pat. Nos. 5,736,368 and 6,051,410 disclose recombinant vaccinia virus strain Wyeth that expresses HIV antigens and proteins. U.S. Pat. No. 5,747,324 discloses a recombinant vaccinia virus strain NYCBH expressing lentivirus genes. EP 0 243 029 discloses a recombinant vaccinia virus strain Western Reserve expressing human retrovirus genes. WO 02/42480 discloses particularly safe and attenuated MVA strains. Recombinant MVA are disclosed inter alia in WO 98/13500 and WO 03/048184.
For the expression of heterologous genes in pox viruses only a few promoters are known to the person skilled in the art, such as the 30K and 40K promoters (see e.g. U.S. Pat. No. 5,747,324), a strong synthetic early/late promoter (see e.g. Sutter et al., Vaccine (1994) 12, 1032-40), the P7.5 promoter (see e.g. Endo et al., J. Gen. Virol. (1991) 72, 699-703) and the promoter derived from the cowpox virus A-type inclusion (ATI) gene (Li et al., J. Gen. Virol. (1998) 79, 613). All of these promoters have been used in recombinant vaccinia viruses to express heterologous genes and were shown to express said genes resulting in the production of the protein encoded by the heterologous gene. Since only a few promoters are available for the expression of genes in vaccinia virus expression systems there is general need for alternative promoters in vaccinia viruses. In addition, all of the promoters known so far are rather strong late promoters, i.e. useful for the expression of genes after the replication of the vaccinia virus vector has occurred. For some application it is desirable to have promoters allowing the expression of genes immediately after the infection of the cells, i.e. there is a need for vaccinia virus early promoters.
Moreover, as pointed out above, MVA is a very promising virus for the expression of heterologous genes due to its improved safety profile. However, all promoters known so far for the expression of heterologous genes in MVA were derived from other vaccinia viruses or are synthetic promoters for the expression in other vaccinia virus. Thus, there is also a need for promoters optimized for the expression in MVA.